PITTSBURGH " Pennsylvania Sen. Bob Casey endorsed Democrat Barack Obama on Friday, a move that could help the presidential candidate make inroads with white working-class voters dubbed "Casey Democrats" in the Keystone State.
Appearing on stage beside the Illinois senator, Casey told a boisterous rally, "I believe in my heart that there is one person who's uniquely qualified to lead us in that new direction and that is Barack Obama."
Pennsylvania's April 22 primary will allocate 158 delegates, the biggest single prize left in the drawn-out nomination battle between Obama and Sen. Hillary Rodham Clinton of New York. Clinton is leading Obama in the state, by 12 points in one poll this month.
Casey is a first-term senator and the son of a popular former governor of the state.
Casey is Catholic and, like his father, is known for his opposition to abortion and support of gun rights. His support could help Obama make inroads among Catholic voters, who have preferred Clinton to Obama in earlier primaries and strongly favor her in Pennsylvania polls.
"I really believe that in a time of danger around the world and in division here at home, Barack Obama can lead us, he can heal us, he can help rebuild America," he said.
Obama told the crowd that he had not pushed Casey hard for an endorsement.
"Bob is such a gracious person and such a thoughtful person that I did not press him on this endorsement," especially since Obama trails Clinton in Pennsylvania polls.
"It would have been easy for Bob just to stay out of it, just to stay neutral, I think everybody would have accepted that," Obama said.
Casey said that he called Clinton Thursday night to tell her of his decision.
"She was very gracious. We know that she's a great senator, she's a great leader," Casey said.
Asked by Casey's endorsement, Clinton spokesman Mo Elleithee said, "We're proud of the support we have from across Pennsylvania, including Gov. (Ed) Rendell, several members of Congress and mayors from across the state.
We look forward to having his support in the general election as Democrats unite to beat John McCain and to turn our country around."
Clinton's backers in the state include Rep. John Murtha, who was an early advocate of withdrawing from Iraq, and Philadelphia Mayor Michael Nutter, who is black.
Meantime, a leading Obama backer, Sen. Patrick Leahy, D-Vt., is saying Clinton should abandon her White House run.
"There is no way that Sen. Clinton is going to win enough delegates to get the nomination," Leahy told Vermont Public Radio in an interview that aired Thursday.
In a statement issued Friday, Leahy, the Senate Judiciary Committee chairman who endorsed Obama in January, said Casey's endorsement of Obama is the latest sign of how the race is going.
"Sen. Clinton has every right, but not a very good reason, to remain a candidate for as long as she wants to. As far as the delegate count and the interests of a Democratic victory in November go, there is not a very good reason for drawing this out. But as I have said before, that is a decision that only she can make," Leahy said.
The Casey endorsement came as Obama began a six-day campaign swing through Pennsylvania.
Pennsylvania has an estimated 3.8 million Catholics, or just over 30 percent of the state's population, and the percentage among Democrats is estimated to be slightly higher.
Obama's team hopes that Casey will help narrow Clinton's huge lead among white working-class voters " men in particular. Clinton routed Obama among that demographic in Ohio and Texas on March 4, raising questions about his electability in November.
In recent weeks, Obama has stressed economic issues important to the middle class, and he is outspending Clinton on television advertising that features blue-collar imagery.
Clinton and her supporters have been making their own direct appeals: backers Kathleen Kennedy Townsend and Robert F. Kennedy Jr., last week wrote a letter to Pennsylvania Catholics emphasizing her plans on health care, mortgage foreclosures and fuel costs. Clinton has been endorsed by Pennsylvania Gov. Ed Rendell, giving her access to his potent political operation.
Obama has lacked a major endorsement by a statewide Pennsylvania politician, and Casey's could help jump-start his Pennsylvania campaign.
Casey has close ties to organized labor, which has been divided in Pennsylvania between the two candidates.
Casey had a 62 percent approval rating among Democrats in a recent Quinnipiac University poll.
Casey's move could also be seen as a political jab at the Clintons. Bill Clinton was the Democrats' presidential nominee in 1992 when Casey's father was not given a prime-time speaking position at the party's convention, which outraged many of the state's conservative Democrats.
Casey was to campaign with Obama as he travels across Pennsylvania by bus.
The bus tour will feature "listening sessions," a technique Clinton used in her 2000 Senate campaign to convince skeptical New Yorkers that she was not just a carpetbagger looking for a plum post after leaving the White House.
Obama hopes to prevent Clinton from racking up a large win in the state which could eat away at his delegate advantage and give her new life in the final primaries running to June.
It may be a tough sell for some in the state, which has a sizable elderly population. In the previous primaries, older Democrats have favored Clinton, while younger voters tend toward Obama.
Casey served two four-year terms as state auditor general. He lost a 2002 gubernatorial bid in the Democratic primary to Rendell.
Casey was elected to the Senate in 2006, defeating conservative GOP incumbent Rick Santorum. Obama campaigned for Casey, but so did Clinton and her husband.
Associated Press Writer Kimberly Hefling in Washington contributed to this report.